Anyone who has worn a white shirt has likely encountered the irksome case of the stubborn yellow armpit stain.

You can beat those pesky stains. And the first step is to know thy enemy.

The yellow stains happen when sebum, oily underarm secretions that come from the hair follicle, isn't washed out of clothing well and forms a yellow stain during the drying process, said Mike Norton, spokesman for Proctor and Gamble, maker of deodorants including the Old Spice and Secret lines.

Antiperspirants can exacerbate the staining because some of their ingredients cling to fabric, providing a layer where the sebum can deposit, Norton said. So even though sebum alone can cause yellow stains, antiperspirants can make them develop faster and yellower.

Fight off stains

Opt for deodorant instead of antiperspirant. The ingredients that sebum clings to are the active ingredients that make antiperspirant effective in the first place, namely aluminum salts such as aluminum zirconium tetrachlorohydrex gly. You're hard-pressed to find antiperspirants without aluminum ingredients, which prevent sweat production by clogging pores.

Deodorants, which mask smell but don't guard against wetness, generally don't contain aluminum. Though deodorants can contain other ingredients that trap sebum, including waxes such as stearyl alcohol and hydrogenated castor oil, they're typically more water soluble than antiperspirants, so they're more easily removed by washing.

Try new antiperspirant technologies. Speed Stick recently launched an antiperspirant called Stainguard, which contains patent-pending "stain defense technology." While it does contain aluminum, it uses a gelling system that keeps the antiperspirant on your skin so it doesn't rub off on your clothes.

Prevent the stains from setting in. After wearing, rinse your shirt's armpit areas in cold water before laundering.

nois.edu/stain) lists removal tips for more than 200 types of stains. Though stains that have been laundered and dried are difficult to remove, several repetitions of the following techniques might be able to conquer them, said Susan Taylor, extension educator for consumer and family economics.

To get rid of perspiration stains, soak the shirt in detergent containing enzymes (it'll say so on the label) for 10 to 15 minutes before laundering it according to the specified fabric instructions. If that doesn't work, pre-treat fresh stains with ammonia and old stains with white vinegar.

For deodorant and antiperspirant stains, scrape off excess material with a blunt knife before soaking the shirt for 15 minutes in a mixture of 1 quart lukewarm water, 1/2 teaspoon liquid hand dishwashing detergent, and 1 tablespoon ammonia. Rub the fabric from the back to loosen the stain, then soak the shirt for another 15 minutes in the same mixture. After rinsing, soak the stain in an enzyme-containing detergent for at least 30 minutes; soak aged stains for several hours. Then launder. If the color stain remains, launder using chlorine or oxygen bleach.